The present invention relates generally to electronic control systems for use in motor vehicles, and more particularly to such an electronic control system having a self-diagnostic function to self-diagnose the occurrence of abnormalities or malfunctions and store and keep data indicative of an operation state at the time of an occurrence of an abnormality.
Attempts to provide a self-diagnostic function to an electronic control system for use in a motor vehicle have been made heretofore, such a technique being disclosed in Japanese Patent provisional Publication No. 62-142849 in which data indicative of an operation state is written in a predetermined area of a random access memory (RAM) at a predetermined time interval so as to self-diagnose the occurrence of abnormalities of input/output devices such as various sensors and actuators. On the basis of the self-diagnostic results showing the occurrence of an abnormality, the electronic control system prohibits the writing operation of the operation state data after the occurrence of an abnormality and stores and keeps the operation state data such as the intake air amount and engine speed immediately before the occurrence of the abnormality.
There is a problem arising in such a conventional self-diagnostic function, however, in that the reliability of the stored data can be deteriorated because the operation state data immediately before the occurrence of an abnormality is arranged to be merely written in the RAM with a battery backup function. In addition, another problem arises in that, in the case of the occurrence of various kinds of abnormalities or the storage of large data, difficulty is encountered to meet the requirements for storing all the necessary data because of shortage of the storage area.